awdinut

I have to change out the heater valve unit in my A8 to, I hope, solve my low heat problem. If you have done yours, I have some questions for you...

Just looking at where the unit is situated it looks like the large, stiff, wire bundles will make it difficult to detatch/attach the hoses. How did you get them out of the way?

And, did you (or wish you had) drain some coolant from the system before you began ?

Any tips or tricks you can share to lessen my pain ?

MP4.2+6.0

I have posted on it before.

On mine I have TWO engine computers there, not just one. First thing I do is unbolt one or both (whatever gets in the way; I forget) and move it aside. I do not unplug it, though I have in the past w/ no ill effects. IIIRC, I also end up removing some or all of a mounting bracket for them, probably to get them out in general.

I have removed it as part of a larger planned job to drain the coolant, though after I played with the valve once I had something goofed up and had to pull it again. That time I don't think i drained it. Regardless, it will spill some coolant in that area and you will need some rags to try to get some of it up. It will run out the plenum drains under the car too.

Suggestion as you do it--change the coolant if you (or somebody) hasn't done it before. Good idea about every 5 years anyway. If you buy Audi OE, you are now stuck with G13. It can still intermix with G12++ though. That was strictly an enviro switch they made--actually for CO2 emissions of all things, not toxicity--so I still prefer G12++. G13 basically has more glycerin in it. If yours is pre about 2007, it may actually have yet older G12+ in it. That I honestly regard as junk and flawed. Audi tried pulling silicates out with G12+ and then basically realized they made a mistake and quietly put them in again with G12++. But they didn't really come clean on what they had done. Silicates in Audis help avoid some internal metal erosion to the heater core and on W12s at least to some head passages (W12's and the underlying VR6 basis for them is sensitive to that in some cooling passages). Now I just buy Pentosin, which is same OE type G12++ formula. Thus, buy enough for a drain and fill, plus a couple gallon jugs of distilled water to do the 50/50 mix. If you go this way, now just drain whole system and pull heater valve while you are at it. Again, if it hasn't been done before, now is a good time to kill the proverbial two birds.

One thing I think of is to realize there are two electrical connectors you can see as you work it loose, but as I recall there is yet one more (three total) that is blind underneath. You can unplug it by hand if you know how to release the connector lock with your fingers, but you want to realize one is there still so you don't go yanking at stuff too much.

When you disassemble, take phone pics as you go to keep track. It is kind of like one of those Chinese wood puzzles and sort of cryptic to reassemble. I only took portions of it apart at a time to minimize confusion. Be careful with the rubber gaskets since there are virtually no piece parts for it; I pinched an o ring on mine when I reassembled; hence the second pull [they may sell that O ring IIRC]. Also, do NOT apply 12V power to the solenoids ever. They are not conventional, but rather pulse width driven. If you 12V power them, they fry.

Last, great time to clean up the plenum. I get in there with my air hose for about ten minutes and chase all the leaves back and forth until they are 98% gone. You can use shop vac some (or reverse the hose to blow air), but a good pressure air hose is best to blow the hidden junk out from under heater box area, master cylinder, etc.